The paradoxical physiology of the narwhal

In a new scientific article published in the highly regarded scientific journal Science, principal author Professor Terrie M. Williams from University of California together with Scientist Mads Peter Heide-Jørgensen from the Greenland Institute of Natural Resources and Scientist Mikkel-Holger S. Sinding describe a paradoxical physiological reaction by narwhals. The study is important for the protection of the oceans around Greenland in connection with, for example, increased marine traffic and oil exploration.

As the first in the world, together with local hunters in Ittoqqortoormiit, the scientists tagged the whales with heart rate monitors, which continuously recorded the heartbeat, swimming activity and geographical position of the animals. The participation of the hunters was crucial, as they have the greatest expertise in capturing the otherwise very shy narwhals alive. The heart rate monitors were attached onto the narwhals’ skin with suction cups. These fell off after three days, after which they could be collected. The results of the collected data left the scientists astounded.

The puzzling whale heart

During an undisturbed dive, the heart of a narwhal normally beats very slowly with 3-4 beats per minute. This is sufficient to supply the whale’s brain and muscles with oxygen. What was surprising in the study was that it also applies to whales in flight: After being caught and equipped with sensors, the narwhals took off to escape under great swimming activity, but at the same time their hearts kept beating slowly. This is very different from other marine and land mammals, either fleeing with increased heart rate or “freezing” with slow heart rate and low muscle activity.

The narwhals apparently have a physiological conflict between their normal diving behaviour with slow heart rate and an escape response with high physical activity that requires a much higher supply of oxygen to the muscles. It costs the whales a lot of energy, but it can also cause permanent damage to vital organs such as the brain. The scientists suspect that the physiological paradox could help shed light on unexplained deaths of deep-diving whales around the world, having been exposed to severe noise. In fact, narwhals use up to 97 % of their oxygen reserves when escaping.

Therefore, it is puzzling that the narwhals’ reaction goes against all knowledge of physiology during flight. It is a response that has been developed in the Arctic without any human influence, but which now can bring the narwhals into conflict with increased marine traffic and industrial activity. The discovery calls for caution in connection with the introduction of new noisy activities in the wake of the ever-reducing ice cover in the narwhals’ habitat.

The study of the narwhal’s physiology is a small piece of a puzzle

The study of the narwhals’ escape response is actually a piece of a big jigsaw puzzle to uncover and understand the stressful effects that man-made disturbances, such as shipping and oil exploration activities, have on the narwhals. Ultimately, the goal for the biologists is to give advice on which stress factors should be taken into account in connection with, for example, exploration for oil and minerals and increased marine traffic.

Heart rate-monitoring tags which among other things recorded the full electrocardiogram from electrodes fitted to the skin of the narwhal. The whales swimming activity and positions were also recorded. The electrodes were attached with suction cups and fell off after three days. Photo: Mads Peter Heide-Jørgensen.